Power circuit for a volatile memory

ABSTRACT

The present description relates to a method and a circuit for powering a volatile memory in which power pulses are sent to the memory, the duration between two pulses being shorter than a remanence time of said volatile memory.

BACKGROUND Technical Field

The present description generally relates to electronic circuits, and more particularly circuits making it possible to supply power to other electronic circuits, for example, a memory circuit.

Description of the Related Art

In general, an electronic device, comprising several electronic circuits, comprises one or more power circuits suitable for powering said circuits composing it. The supply of each of these circuits can be done in a different manner. As an example, some circuits use a continuous power supply, while other circuits, for example, use a periodic power supply. One drawback of a continuous power supply is that it is costly in terms of energy.

Memory circuits, or memories, are circuits configured to store data; several types exist. Certain memories, non-volatile memories, are configured to store data when they are not supplied with energy, while others, volatile memories, receive a continuous supply of power to store data. Volatile memories are therefore very costly memories in terms of energy.

It would be desirable to be able to improve, at least in part, certain aspects of the known power circuits, and more particularly certain aspects of the known power circuits of memory circuits.

BRIEF SUMMARY

One or more embodiments of the present application provide better performing power circuits and memory circuits with lower energy consumption.

One embodiment offsets all or some of the known drawbacks of the known power circuits, and more particularly certain aspects of the known power circuits of memory circuits.

One embodiment provides a power circuit of a volatile memory in which power pulses are sent to the memory, the duration between two pulses being shorter than a remanence time of said volatile memory.

One embodiment provides a power supply method of a volatile memory in which power pulses are sent to the memory, the duration between two pulses being shorter than a remanence time of said volatile memory.

According to one embodiment, the volatile memory is a dynamic volatile memory.

According to one embodiment, said duration is between 55 and 75% of the remanence time.

According to one embodiment, the pulses are periodic.

According to one embodiment, the pulses have a duration on the order of 100 nanoseconds.

According to one embodiment, the duration between two pulses is adjusted by a processor.

According to one embodiment, a memory of the processor contains the remanence time of the volatile memory.

According to one embodiment, a signal indicating a malfunction of the processor interrupts the power supply of the volatile memory.

According to one embodiment, the remanence time of the volatile memory is the duration during which data stored in the memory are kept after stopping a power supply of the memory.

One embodiment provides a device comprising:

-   -   a processor;     -   a volatile memory; and     -   a power circuit of the memory.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

FIG. 1 shows, very schematically and in block form, part of an embodiment of an electronic device; and

FIG. 2 shows a timing diagram illustrating power and control signals.

DETAILED DESCRIPTION

Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the general operation of a memory, and more particularly of a volatile memory, will not be described hereinafter.

Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements linked or coupled together, this signifies that these two elements can be connected or they can be linked or coupled via one or more other elements.

In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “higher”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures.

Unless otherwise specified, the expressions “around”, “approximately”, “substantially” and “on the order of” mean to within 10%, preferably to within 5%.

FIG. 1 shows, very schematically and in block form, an electronic device 100 according to one embodiment.

The device 100 comprises:

-   -   a volatile memory 102 (RAM); and     -   a power circuit 104 (POWER MGT) for managing the volatile memory         102;     -   a power source 106 (POWER); and     -   a processor 108 (CPU).

The volatile memory 102, random-access memory (RAM), is a memory that receives power from a power source to store data. Once the power source is cut, the data stored in the volatile memory 102 are no longer accessible; they are generally lost and/or erased. However, the loss of these data is not instantaneous; after the power is cut, the data stored in the volatile memory 102 are still present for a period, called remanence time Tr, which is the time for all of the charges to disappear from the memory circuit by leakage. According to the volatile memory models, the remanence time Tr can, for example, be on the order of 500 nanoseconds to 1 millisecond at ambient temperature and reach up to 30 milliseconds at a temperature of −40° C.

In the described embodiments, advantage is taken of what can be compared to a defect or artifact of the volatile memory, namely the remanence of the information, so as only to power the memory discontinuously. The remanence time is determined for a given type, category or model of volatile memory, by simulation and/or in situ measurements, etc.

The remanence time Tr originates from a feature of volatile memories. The memory 102 is characterized in that its remanence time Tr has been calculated. As an example, the volatile memory is a dynamic volatile memory, for example, of the DRAM (Dynamic Random Access Memory) type.

According to the described embodiment, the volatile memory 102 receives a power signal Valim from the power circuit 104. The volatile memory further receives control signals, for example, read and/or write signals, but they are not shown or described here.

The power circuit 104 is a circuit configured to provide the power signal Valim to the memory 102. The power circuit 104 receives:

-   -   a control signal CMD from the processor 108;     -   a state signal STATE, which may indicate a malfunction of the         processor 108, from the processor 108; and     -   a DC voltage Vdd from the power source 106.

The power source 106 is a continuous power source. As an example, the power source can be a main power circuit of the device.

The processor 108 is, for example, a processor included in the device and distinct from the circuit 104.

The operation of the part 100 of the device, and the signals Valim, CMD and STATE, will be described hereinafter. FIG. 2 is a timing diagram illustrating the evolution of the signals Valim and STATE described in connection with FIG. 1.

The signal Valim is a power signal comprising power pulses I separated by a duration T1. The power pulses I are, for example, voltage pulses and/or current pulses. According to one embodiment (shown in FIG. 2), the pulses I are spaced apart periodically by the duration T1. The duration T1 is shorter than the remanence time Tr of the volatile memory 102. As an example, the duration T1 is equal to about 55 to 75% of the remanence time Tr. Each pulse I has a duration sufficient to provide the memory 102 with power to keep the data that it stores. As an example, the pulses I have a duration, for example, of between 100 and 200 nanoseconds. As an example, the duration of the pulses I is adjusted by the power circuit 104.

The state signal STATE is a signal indicating a malfunction of the processor 108 to the power circuit 104. When the processor is working correctly, the state signal STATE has no influence over the power of the memory 102. However, when the processor 104 does not work correctly, for example, when it is the victim of a malicious attack, the state signal STATE controls the power circuit 104 to cut the power supply of the memory 102, such that the data that it stores are no longer accessible.

According to the embodiment illustrated in FIG. 2, the state signal STATE is an analog signal comprising power pulses spaced regularly apart, for example, periodically, by a duration T2. According to this example, the duration T2 is shorter than the duration T1, such that when the operating frequency of the processor decreases, for example, during a malicious attack, the duration T2 exceeds the duration T1, which would be a sign of attack of the processor 108 for the power circuit 104.

As a variant, the state signal STATE is an analog signal having a different form from that previously described. According to another variant, the state signal STATE can be a digital signal.

The operation of the part 100 of the device described in connection with FIG. 1, and a method for supplying power to the memory 102, are as follows.

The processor 108 knows the remanence time Tr of the memory 102, for example, including a memory in which the remanence time is stored, and indicates, to the power circuit 104, via the control signal CMD, the duration T1 between the pulses of the power signal Valim. In other words, the processor 108 sets or adjusts the duration T1. The control signal CMD can be an analog signal or a digital signal. The power circuit 104 further receives the state signal STATE, allowing it to be alerted in case of operating problem and/or attack of the processor 108. The power circuit 104 generates the signal

Valim, from the DC voltage Vdd received from the power source 106, and the control signal CMD. As previously stated, the signal Valim is configured to power the memory 102 by power pulses before the remanence time Tr has elapsed so that the memory 102 does not lose the data that it stores.

One advantage of this embodiment is that the volatile memory 102 is no longer powered by a continuous power supply, but by a periodic power supply that is less costly in terms of energy.

Another advantage of this embodiment is, for example, in case of attack of the device, that the erasure of data stored in the memory 102 is faster than when the memory 102 is powered continuously. Indeed, the actual time taken by the memory 102 to lose/erase the data that it stores is less than or equal to its remanence time Tr. More particularly, when the power supply of the memory 102 is cut after a pulse I arrives, the loss time of the data is equal to the remanence time, but when the power supply is cut later, the loss time of the data is therefore shorter than the remanence time Tr, since it is the last pulse I received by the memory 102 that serves as the starting point for the remanence time.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art.

Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove.

The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

1. A power circuit configured to send a plurality of power pulses to a volatile memory, consecutive pulses of the plurality of power pulses being separated by a duration that is shorter than a remanence time of said volatile memory.
 2. The power circuit according to claim 1, wherein said duration is between 55 and 75% of the remanence time.
 3. The power circuit according to claim 1, wherein the pulses are periodic.
 4. The power circuit according to claim 1, wherein the pulses have a duration of approximately 100 nanoseconds.
 5. The power circuit according to claim 1, wherein the power circuit is configured to adjust the duration between consecutive pulses based on a signal from a processor.
 6. The power circuit according to claim 1, wherein the power circuit is configured to interrupt supply of power to the volatile memory in response to a signal indicating a malfunction of the processor.
 7. The power circuit according to claim 1, wherein the remanence time of the volatile memory is the duration during which data stored in the memory are kept after stopping a power supply of the volatile memory.
 8. A method, comprising powering a volatile memory by sending a plurality of power pulses to the volatile memory, consecutive power pulses of the plurality of power pulses being separated by a duration that is shorter than a remanence time of said volatile memory.
 9. The method according to claim 8, wherein a memory of the processor stores the remanence time of the volatile memory, and the processor controls the duration between the consecutive power pulses based on the stored remanence time.
 10. The method according to claim 8, wherein said duration is between 55 and 75% of the remanence time.
 11. The method according to claim 8, wherein the pulses are periodic.
 12. The method according to claim 8, wherein the pulses have a duration of approximately 100 nanoseconds.
 13. The power circuit 1, wherein the power circuit is configured to interrupt supply of power to the volatile memory in response to a signal indicating a malfunction of the processor.
 14. A device comprising: a processor; a volatile memory; and a circuit configured to send a plurality of power pulses to the volatile memory, consecutive pulses of the plurality of power pulses being separated by a duration that is shorter than a remanence time of said volatile memory.
 15. The device according to claim 14, wherein the volatile memory is a dynamic volatile memory.
 16. The device according to claim 14, wherein the processor includes a memory that stores the remanence time of the volatile memory, and the processor controls the duration between the consecutive power pulses based on the stored remanence time.
 17. The device according to claim 14, wherein said duration is between 55 and 75% of the remanence time.
 18. The device according to claim 14, wherein the pulses are periodic.
 19. The device according to claim 14, wherein the pulses have a duration of approximately 100 nanoseconds.
 20. The device according to claim 14, wherein the power circuit is configured to interrupt supply of power to the volatile memory in response to a signal indicating a malfunction of the processor. 